In the polymerization of fluoromonomers, traditionally the monomers are added to a kettle along with an initiator, to initiate the polymerization, as well as a solvent, and in the case of aqueous emulsion polymerization, the polymerization is carried out in water and typically in the presence of an emulsifier in order to stabilize the emulsion.
Fluorinated sulfinic acids and their salts have been used to initiate polymerization. The fluorinated sulfinic acids and their salts have been used along with oxidizing agents during polymerization of fluoromonomers as a means for achieving perfluorinated end groups, which may offer the advantages of more stability, improved performance, etc. by reducing or eliminating the less stable polar end-groups. As disclosed in Grootaert (U.S. Pat. No. 5,285,002), the fluorinated sulfinic acid or salt thereof reacts with an oxidizing agent to generate a fluorinated alkyl radical via electron transfer, which then initiates the polymerization of monomers.
Various papers have described how to prepare fluorinated sulfinic acids or their salts by reduction of sulfonyl fluoride with different reducing agents or by dehalosulfination reaction from fluorinated halides. Examples of different reducing agents used to reduce a sulfonyl fluoride are NH2NH2 as described in U.S. Pat. No. 2,950,317 (Brown et al.), M2SO3 and NaBH4 as described in U.S. Pat. No. 5,285,002 (Grootaert), and K2SO3 as described in U.S. Pat. No. 5,639,837 (Farnham et al.). Examples of a dehalosulfination reaction from fluorinated halides are described by Huang et al. in Journal of Fluorine Chemistry, vol. 23 (1983) p. 193-204 and p. 229-240; by Huang et al. in Chinese Journal of Chemistry, vol. 9 (1991) p. 351-359, and Fan-Hong et al., in Journal of Fluorine Chemistry, vol. 67 (1994) 233-234.